The day of the Japanese attack on Pearl Harbor in December 1941, President Franklin D. Roosevelt signed Executive Order 2525. Under the order, the federal government was empowered to apprehend and confine “alien enemies,” a measure that resulted in the internment of thousands of Japanese immigrants and Japanese American citizens in camps mostly west of the Rockies.

Fred Korematsu, a 23-year-old American citizen, was ordered to go to one of those camps in 1942. He refused, pleading his case in the courts until the Supreme Court resolved the issue. In the 1944 case Korematsu v. United States, the court ruled 6-3 in favor of the government, determining that the president’s national security argument allowed the executive order to stand.

That decision was officially rejected by the Supreme Court on Tuesday as part of Trump v. Hawaii, the court’s upholding of President Trump’s ban on migration from certain mostly Muslim countries.

“The dissent’s reference to Korematsu . . . affords this Court the opportunity to make express what is already obvious,” Chief Justice John G. Roberts Jr. wrote in his majority opinion. “Korematsu was gravely wrong the day it was decided, has been overruled in the court of history, and — to be clear — ‘has no place in law under the Constitution.’ ”

Roberts was responding to a dissent from Justice Sonia Sotomayor that alleged “stark parallels” between the Korematsu decision and Roberts’s majority opinion in Trump.

“Whatever rhetorical advantage the dissent may see in doing so,” Roberts wrote, “Korematsu has nothing to do with this case.”

As part of the Supreme Court’s travel ban decision, a precedent that upheld the forcible transfer of Japanese Americans to internment camps was rejected. (Deanna Paul, Melissa Macaya/The Washington Post)

University of Michigan law professor Richard Primus wrote an article exploring precisely the overlap between Korematsu and the travel ban in May 2017. When he revisited that article in April, he noted that “the deepest lesson of Korematsu is one that ought to make us unsurprised if the Supreme Court upholds the entry ban orders” — to wit, that the court “is perfectly capable of signing off on morally evil executive branch policies that are ostensibly (but not really) necessary for national security, even when the legal arguments for the executive branch are weak.”

That appears to have been the rationale behind Tuesday’s action. We spoke with Primus by phone to explore the history of Korematsu and its applicability to Trump.

Primus first reinforced that Roberts’s assessment of Korematsu was a common one in the legal community.

Korematsu until now had never been officially overruled,” he said, “but as a practical matter it was a repudiated decision. Well-socialized lawyers have known for more than half a century that you don’t rely on Korematsu because it’s shameful and, within a short time after it was decided in 1944, there came to be a consensus that the decision in Korematsu was a stain on the Supreme Court — a stain like Plessy v. Ferguson or Dred Scott v. Sandford.” Primus noted that Roberts’s use of “wrong on the day it was decided” echoed what the Supreme Court said in 1992 about Plessy.

During the campaign, Trump himself pointed to Japanese internment as a precedent for his proposed ban on Muslim migration to the United States. Lawyers associated with his campaign, Primus said, pointed to Korematsu as a precedent defending the idea — a move that Primus called “shocking.”

During his tenure as president, that hasn’t happened.

“The professional lawyers for the United States from the Department of Justice know better than to walk into court and say, ‘You should rule for us on the authority of Korematsu,’ ” he said. “Instead, what they have to do is say, ‘Korematsu is nothing like this case.’ ”

Sotomayor’s dissent, though, argues that there are specific parallels.

“As here, the Government invoked an ill-defined national security threat to justify an exclusionary policy of sweeping proportion. . . . As here, the exclusion order was rooted in dangerous stereotypes about, inter alia, a particular group’s supposed inability to assimilate and desire to harm the United States. . . . As here, the Government was unwilling to reveal its own intelligence agencies’ views of the alleged security concerns to the very citizens it purported to protect. . . . And as here, there was strong evidence that impermissible hostility and animus motivated the Government’s policy.”

The point about revealing intelligence information is important. In 2011, the Justice Department admitted that “a key intelligence report that undermined the rationale behind the internment” had never been presented to the Supreme Court during Korematsu. Instead, the solicitor general at the time among other things “relied on gross generalizations about Japanese Americans, such as that they were disloyal and motivated by ‘racial solidarity.’ ”

The 1944 Korematsu decision attempted to sideline the issue of race.

“Our task would be simple, our duty clear, were this a case involving the imprisonment of a loyal citizen in a concentration camp because of racial prejudice,” that decision concludes. “Regardless of the true nature of the assembly and relocation centers . . . we are dealing specifically with nothing but an exclusion order. To cast this case into outlines of racial prejudice, without reference to the real military dangers which were presented, merely confuses the issue.”

In Trump v. Hawaii, the issue of prejudice is trickier.

“As in Korematsu, there are really powerful indications that the policy is motivated by animus,” Primus said. “As a factual matter, the entry ban would not exist without Trump’s bigotry toward Muslims. Justice Sotomayor is saying that — and even the majority doesn’t deny that. The majority says irrespective of the president’s articulated attitudes, the question we should answer is just whether this policy could be serving a legitimate interest.”

Sotomayor’s dissent, Primus said, argues that “we are again giving the executive government a pass on an animus-based measure because the executive branch is hiding behind a national security claim.”

Both Roberts and Justice Anthony M. Kennedy in a concurring opinion seem to argue that they have concerns about the motivations underlying the ban, Primus said.

“The majority recognizes that the president has expressed ugly anti-Muslim attitudes,” he said. “Both the majority and the Kennedy concurrence all but come out and say the president is expressing attitudes that are contrary to American constitutional values. It just doesn’t follow for them that they should consider the order to have unconstitutional motivations.”

Why not? Because the executive order doesn’t explicitly point to race or religion.

If a law includes discriminatory language on its face (as in an affirmative action policy) the courts apply “strict scrutiny.” But since the travel ban didn’t explicitly use discriminatory language, the court used a looser standard that, in essence, gives the administration the benefit of the doubt.

“In evaluating this argument, one needs to remember that everyone knows that it is settled doctrine that discrimination on the face of the order invokes strict scrutiny,” Primus said, “so no minimally competent government drafter will write the discrimination into the face of the order.”

“If all that doctrine means is, ‘don’t put it on the face of the order,’ ” he said, “it actually isn’t so helpful.”

“The majority’s opinion works by divorcing the order from the president and his actual attitudes and motivations,” he added. Rather, it is considered largely through the lens of Trump’s national security powers and, through that lens, is upheld.

Primus was blunt in his assessment of that decision.

“It is an important premise in the constitutional system that the president gets a lot of deference in national security,” he said. But, he added, “that deference has long been premised on the assumption that presidents are intelligent, informed, responsible people.”

“This case raises the question of when deference becomes abdication,” he said. “It’s one thing to give the president the benefit of the doubt in national security cases. In this case the doubt about the motivations [on the part of the court] is manufactured.”

Sotomayor concluded her dissent by again linking the majority opinion back to Korematsu.

“By blindly accepting the Government’s misguided invitation to sanction a discriminatory policy motivated by animosity toward a disfavored group, all in the name of a superficial claim of national security,” she wrote, “the Court redeploys the same dangerous logic underlying Korematsu and merely replaces one ‘gravely wrong’ decision with another.”